Pneumatic tire and method of improving high-speed RFV thereof

ABSTRACT

A method of improving high-speed radial force variation of a pneumatic tire is disclosed. The tread portion is provided on the radially inner surface with an elastic patch. The weight and position of the patch determined based on (A) a low-speed fundamental RFV or (B) a low-speed fundamental RRO or (C) a weight imbalance of the tire. In case (A), the position is a point of the minimum low-speed fundamental RFV and the weight is {(F×TR)/33 2 }×1000×a 1 . In case (B), the position is a point of the minimum low-speed fundamental RRO and the weight is {(RO×TR)/33 2 }×1000×a 2 . In case (C), the position is a light weight position and the weight UB×(RR/TR)×a 3 . Here, TR is the radius in meter of the tire, 
     F is the maximum variation of the low-speed fundamental RFV, 
     RO is the maximum variation of the low-speed fundamental RRO, 
     RR is the radius of the wheel rim, 
     UB is the tire imbalance, 
     a 1  is coefficient in a range of from 0.5 to 3.0, 
     a 2  is a coefficient in a range of from 100 to 400, 
     a 3  is a coefficient in a range of from 0.5 to 2.0.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of improving the high-speedradial force variation of a pneumatic tire and a pneumatic tire havingimproved high-speed radial force variation.

2. Description of the Related Art

The radial force variation (RFV), radial runout (RRO) weight imbalanceof a pneumatic tire are well known factors in tire vibrations duringrunning, and they are mutually related to a high degree. Generally,various standards relating to tire uniformity tests such as the Japanesestandard JASO C607-87 refer to the RFV and RRO measured at a relativelyslow speed at which the centrifugal force can be disregarded(hereinafter low-speed RFV and low-speed RRO).

Even if such low-speed RFV and low-speed RRO and the weight imbalance ata relatively slow rotational speed are improved, there is still apossibility that vibrations occur during high-speed running over 80km/h.

SUMMARY OF THE INVENTION

Thus, the inventor studied and found that a chief factor in the tirevibrations is the fundamental wave or harmonic of the RFV duringhigh-speed running (hereinafter high-speed fundamental RFV).

Therefore, a primary object of the present invention is to improve thehigh-speed RFV of a pneumatic tire without affecting the low-speed RFVand RRO.

According to one aspect of the present invention, a tread portion of apneumatic tire is provided on the radially inner surface with an elasticpatch, the patch having a certain weight and being stuck at a certaincircumferential position, the weight and position are determined basedon (A) low-speed fundamental RFV or (B) low-speed fundamental RRO or (C)static weight imbalance of the tire, each measured before applying thepatch.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described in detailin conjunction with the accompanying drawings.

FIG. 1 is a cross sectional view of a pneumatic tire according to thepresent invention.

FIG. 2 is a perspective view showing an example of the patch.

FIG. 3 is a schematic cross sectional view of the tire taken along thetire equator.

FIG. 4 is a graph showing a low-speed fundamental RFV.

FIG. 5 is a graph showing a low-speed fundamental RRO.

FIG. 6 is a diagram for explaining the static weight imbalance of thetire.

DETAILED DESCRIPTION

According to the present invention, a pneumatic tire 1 is provided witha patch 10. The patch 10 is stuck on the radially inner surface HS ofthe tread portion 2, and as explained hereunder, its position P andweight M are determined based on (A) low-speed fundamental RFV or (B)low-speed fundamental RRO or (C) weight imbalance of the tire, eachmeasured before applying the patch.

The pneumatic tire 1, as the subject of the present invention, includesvarious tires such as the usual vulcanized rubber tire which has ahollow to be filled with air, and has easy access the radially innersurface HS of the tread portion 2.

FIG. 1 shows such a vulcanized rubber tire which is composed of theabove-mentioned tread portion 2, a pair of axially spaced bead portions4 and a pair of sidewall portions 3 extending therebetween. Thisparticular example is a tubeless radial tire for passenger cars of whichthe inner surface HS is covered with an inner liner 8 made ofair-impermeable rubber.

The patch 10 is a sheet of an elastic material made of, e.g., vulcanizedrubbers, synthetic resins and the like. The JIS hardness measured with atype-A durometer is preferably less than 60 degrees.

The patch 10 may be formed in various shapes, e.g., circle, ellipse,rectangle, square and the like. In this embodiment, the shape is anellipse or a rectangle whose corners are rounded, as shown in FIG. 2.

If the circumferential position P is determined, the patch 10 is fixedby means of adhesive agent so as to center on the position P withrespect to the circumferential direction and center on the tire equatorC with respect to the axial direction.

In case of the patch made of rubber, a rubber cement ofself-vulcanization type can be preferably used for the adhesive agent.But, various adhesive agents can be used.

The thickness t, length L and width W of the patch 10 depend on itsweight M. But, it is preferable for controlling a decrease in the tireuniformity that: the thickness t is less than 2.0 mm but not less than1.0 mm; the circumferential length L is less than 300 mm but not lessthan 50 mm; and the axial width W is less than the width BW of a treadreinforcing belt 7 but not less than 25 mm.

(A) Determination of position and weight based on Low-speed fundamentalRFV

The radial force variation (RFV) of the tire is measured at a relativelyslow rotational speed of 60 rpm. This speed corresponds to acircumferential velocity of about 7 km/h in the case of passenger cartires. The circumferential velocity may be increased up to about 15 km/has far as the centrifugal force does not affect the measurement.

For the method of measuring the RFV, “Testing method for automobile tireuniformity”, Japanese Automobile Standards Organization, C607-87, can beadopted.

FIG. 4 shows an example of the radial force variation per one revolutionin which short-cycle fluctuations or higher harmonics were cut off andthus only the fundamental harmonic is shown.

According to this fundamental harmonic, the position P is determined asa minimum point P1 at which the radial force is minimum, and the maximumvariation F is determined as the difference between the maximum radialforce and the minimum radial force.

Using the maximum variation F in Newtons and the radius TR of the tirein meters, the weight M1 in gram of the patch 10 is determined by thefollowing equation

M 1={(F×TR)/33²}×1000×a 1

wherein

a1 is a coefficient. The coefficient a1 is set in the range of from 0.5to 3.0, preferably, in the range of from 0.5 to 1.5.

Comparison Test

A pneumatic tire (size 205/65R15) without the patch was measured for thelow-speed fundamental RFV at the circumferential velocity of 7 km/h.Then, changing the position and coefficient al, the patch was applied tothe same tire and the low-speed RFV and high-speed RFV were measured atthe circumferential velocity of 7 km/h and 120 km/h, respectively,according to JASO C607-87. The inner pressure and tire load were 200 kPaand 4.9 KN, respectively.

TABLE 1 Patch none Position* — P P C C Weight M1(g) 0 8 17 8 17Coefficient al — 0.5 1 0.5 1 Low-speed fundamental RFV (N) 57 62 59 6157 High-speed fundamental RFV (N) 59 35 29 84 100 *P: Proper positionP1, C: Counter position TR = 0.32 m

It was confirmed that the tire properly provided with the patch can begreatly improved in the high-speed fundamental RFV without affecting thelow-speed fundamental RFV substantially.

If the coefficient al is less than 0.5, it is difficult to reduce thehigh-speed fundamental RFV. If the coefficient al is more than 3.0, itbecomes necessary to increase the counter balance weight to be appliedto the wheel rim on which the tire is mounted. And there is apossibility of deteriorating the fundamental RFV by contraries.

(B) Determination of Position and Weight Based on Low-speed FundamentalRRO

The radial runout (RRO) of the tire is measured at a relatively slowrotational speed of 60 rpm. The circumferential velocity may beincreased up to about 15 km/h as far as the centrifugal force does notaffect the measurement.

For the method of measuring the RRO, “Testing method for automobile tireuniformity”, Japanese Automobile Standards Organization, C607-87, can beadopted.

FIG. 5 shows an example of the radial runout per one revolution in whichhigher harmonics and similar fluctuations were cut off, and thus onlythe fundamental harmonic is shown.

According to this fundamental harmonic, the position P is determined asa minimum point P2 at which the radial runout is minimum, and themaximum variation RO (mm) is determined as the difference between themaximum radial runout and the minimum radial runout.

Using the maximum variation RO in millimeter and the radius TR of thetire in meter, the weight M2 in gram of the patch 10 is determined bythe following equation

M 2={(RO×TR)/33²}×1000×a 2

wherein

a2 is a coefficient. The coefficient a2 is set in the range of from 100to 400, preferably, in the range of from 100 to 200.

Comparison Test

A pneumatic tire (size 205/65R15) without the patch was measured for thelow-speed fundamental RRO at the circumferential velocity of 7 km/haccording to JASO C607-87. Then, the position P and weight M2 weredetermined using the coefficient a2 being 200, and the patch was appliedto the tire and the low-speed RFV and high-speed RFV were measured atthe circumferential velocity of 7 km/h and 120 km/h in the same manneras above. The inner pressure and tire load were 200 kPa and 4.9 KN,respectively.

TABLE 2 Patch none Weight M2(g) 0 22 Coefficient a2 200 Low-speedfundamental RRO (mm) 0.4 0.4 Low-speed fundamental RFV (N) 51 53High-speed fundamental RFV (N) 60 31 TR = 0.32 m

It was confirmed that the tire properly provided with the patch can begreatly improved in the high-speed fundamental RFV without affecting thelow-speed fundamental RRO and the low-speed fundamental RFVsubstantially.

If the coefficient a2 is less than 100, it is difficult to reduce thehigh-speed fundamental RFV. If the coefficient a2 is more than 400, itbecomes necessary to increase the counter balance weight to be appliedto the wheel rim on which the tire is mounted. Further, there is apossibility of deteriorating the fundamental RFV.

(C) Determination of Position and Weight Based on Weight Imbalance

As schematically shown in FIG.6, the test tire is mounted on a wheel rim21 having no weight imbalance and supported frictional free to allow thetire and wheel rim assembly to free rotate by the gravity. When the tireis stopped by itself, the uppermost point is defined as the lightposition P3, and the lowermost point as the heavy position K.

A weight imbalance UB is defined as the value of a weight which canbalance with the imbalance of the tire when applied to a particularposition on a straight line drawn between the light position P3 andheavy position K. This particular position is spaced apart from therotational axis towards the light position P3 by a distance RR (m). Asthe distance RR (m) the radius of the wheel rim or a half of the rimdiameter, namely a half of the tire bead diameter is used.

Using the weight imbalance UB in grams, the distance RR in meters andthe radius TR of the tire in meters, the weight M3 in grams of the patch10 is determined by the following equation

M 3=UB×(RR/TR)×a 3

wherein

a3 is a coefficient. The coefficient a3 is set in the range of from 0.5to 2.0, preferably in the range of from 0.5 to 1.5. In this case, theposition P is the light position P3. Thus, the patch 10 having theweight M3 is applied to the light position P3.

Comparison Test

On a pneumatic tire (size 275/70R16) not provided with the patch, thelight position P3 and the weight imbalance UB was found out, and theweight M3 of the patch 10 was determined thereby. Then, the patch wasapplied to the tire and the low-speed RFV and high-speed RFV weremeasured at the circumferential velocity of 7 km/h and 120 km/haccording to JASO C607-87. The inner pressure and tire load were 200 kPaand 4.9 KN, respectively.

TABLE 3 Patch none Weight M3(g) 0 18 Coefficient a3 1 Weight imbalanceUB (g) 35 6 Low-speed fundamental RFV (N) 63 62 High-speed fundamentalRFV (N) 95 81 RR = 0.2 m, TR = 0.39 m

It was confirmed that the tire provided with the patch can be greatlyimproved in the high-speed fundamental RFV without affecting thelow-speed fundamental RFV.

If the coefficient a3 is less than 0.5, it is difficult to reduce thehigh-speed fundamental RFV. If the coefficient a3 is more than 2.0, itbecomes necessary to increase the counter balance weight to be appliedto the wheel rim on which the tire is mounted. Further, there is apossibility of deteriorating the fundamental RFV.

By the above-mentioned tests made relating to the determinations (A),(B) and (C), the following observations are also confirmed. As to (A),the reduction of the high-speed fundamental RFV is effective when themaximum variation F of the low-speed fundamental RFV is more than 50 N,but not effective when F is less than 30 N. As to (B), the reduction ofthe high-speed fundamental RFV is effective when the maximum variationRO of the low-speed fundamental RRO is more than 1.3 mm, but noteffective when RO is less than 0.15 mm. As to (C), the reduction of thehigh-speed fundamental RFV is effective when the weight imbalance UB ismore than 40 g, but not effective when UB is less than 10 g. Further,the reduction is effective if the light position P3 is far from themaximum point of the low-speed fundamental RFV or RRO, but not effectiveif the light position P3 is near the maximum point.

If the thickness t is more than 2.0 mm, the rigidity differenceundesirably increases in the patched portion. If the length L is morethan 300 mm, the high-speed fundamental RFV can not be reduced becausethe centrifugal force acts on a wide range. If the width W is more thanthe belt width BW, the ground pressure is increased in the treadshoulder portions and as a result uneven wear and heat generation arepromoted in these portions.

What is claimed is:
 1. A method of improving a high-speed RFV of apneumatic which comprises: providing the pneumatic tire comprising atread portion having a radially inner surface; providing an elasticpatch to be stuck on said radially inner surface of the tread portion;measuring a low-speed fundamental RFV of the tire to determine a minimumpoint at which the low-speed fundamental RFV becomes minimum, and toobtain the maximum variation F in Newton between the maximum value andthe minimum value of the measured low-speed fundamental RFV; determininga position of the elastic patch to be stuck as being a circumferentialposition on said radially inner surface corresponding to said minimumpoint; determining a weight in grams of the elastic patch to be stuck asa value obtained by the following equation: {(F×TR)/33²}×1000×a 1wherein TR is the radius in meters of the tire and a1 is coefficient ina range of from 0.5 to 3.0; adjusting the elastic patch to thedetermined weight; and sticking the weight adjusted elastic patch atsaid determined position on said radially inner surface of the treadportion.
 2. The method according to claim 1, wherein the coefficient a1is in a range of from 0.5 to 1.5.
 3. The method according to claim 1,wherein in measuring the low-speed fundamental RFV of the tire, therotational speed of the tire is 60 rpm.
 4. The method according to claim2, wherein in measuring the low-speed fundamental RFV of the tire, arotational speed of the tire is 60 rpm.
 5. A method of improving ahigh-speed RFV of a pneumatic tire, which comprises: providing thepneumatic tire comprising a tread portion having a radially innersurface; providing an elastic patch to be stuck on said radially innersurface of the tread portion; measuring a low-speed fundamental RRO ofthe tire to determine a minimum point at which the low-speed fundamentalRRO becomes minimum, and to obtain the maximum variation RO inmillimeters between the maximum value and the minimum value of themeasured low-speed fundamental RRO; determining a position of theelastic patch to be stuck as being a circumferential position on saidradially inner surface corresponding to said minimum point; determininga weight in grams of the elastic patch to be stuck as a value obtainedby the following equation: {(RO×TR)/33²}×1000×a 2 wherein TR is a radiusin meters of the tire and a2 is a coefficient in a range of from 100 to400; adjusting the elastic patch to the determined weight; and stickingthe weight adjusted elastic patch at said determined position on saidradially inner surface of the tread portion.
 6. The method according toclaim 5, wherein the coefficient a2 is in a range of from 100 to
 200. 7.The method according to claim 5, wherein in measuring the low-speedfundamental RRO of the tire, a rotational speed of the tire is 60 rpm.8. The method according to claim 6, wherein in measuring the low-speedfundamental RRO of the tire, a rotational speed of the tire is 60 rpm.9. A method of improving a high-speed RFV of a pneumatic tire, whichcomprises: providing the pneumatic tire comprising a tread portionhaving a radially inner surface; providing an elastic patch to be stuckon said radially inner surface of the tread portion; examining a staticweight imbalance of the tire to find a lightweight position of the tirearound the tire axis; determining a value UB in grams of a weight whichcan statically balance with the weight imbalance of the tire around thetire axis when the weight is applied at a distance equal to RR towardssaid lightweight position from the tire axis, wherein RR is the radiusin meters of a wheel rim for the tire; determining a position of theelastic patch to be stuck as being a circumferential position on saidradially inner surface corresponding to said lightweight position;determining a weight in grams of the elastic patch to be stuck as avalue obtained by the following equation: {UB×(RR/TR)×a 3} wherein TR isa radius in meters of the tire and a3 is a coefficient in a range offrom 0.5 to 2.0; adjusting the elastic patch to the determined weight;and sticking the weight adjusted elastic patch at said determinedposition on said radially inner surface of the tread portion.
 10. Amethod according to claim 9, wherein the coefficient a3 is in a range offrom 0.5 to 1.5.